Developing electrostatic images with a liquid developer



y 27, 1959 KARL-HEINZ DEGENHARDT ETAL 3,446,649

DEVELOPING ELECTROSTATIC IMAGES WITH A LIQUID DEVELOPER Filed Sept. 5,1964 FIG.2

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I N VENTORS lfar/ hz'nz Dam/70rd! y GET/I070 Marx United States Patent 0Filed Sept. 3, 1964, Ser. No. 394,186 priority, application Germany,Sept. 5, 1963,

K 50,739 Int. Cl.

B441] 1/18; 1305b 5/02 US. Cl. 117-37 5 Claims The present inventionrelates to a process for developing electrostatic fields by means of arelative motion between the surface of a material carrying theelectrostatic field and a wetting developer which is contained within alinear gap and is in contact with the aforementioned surface.

The present inVentiOn further relates to a device for carrying out thisprocess.

In wetting development, use is made of the changes in the adhesivestress of the developing liquid on the surface to be developed, thechanges in adhesive stress being due to the imagewise differentiatedcondition of the surface which carries an electrostatic field.

Wetting developers are liquids, the composition of which is such thatthey wet the material to be developed only in the areas carrying anelectrostatic field. Apart from the selection of the developing liquids,it is desirable in this process to apply the developing liquid to thematerial carrying the electrostatic field in such a way that a rapidwetting and development of the image areas is effected without applyingtoo large'an amount of excess developer which could remain attached bypurely mechanical adhesion and in an undesired manner even to thoseareas which should not be contacted with the developer.

Furthermore, the developing method should provide the possibility ofproducing reversal images by applying an additional potential during thedeveloping process. For

(Claims this reason as well, an excess of developing liquid must beavoided so that the developer can not come into contact with the back ofthe material, which would result in a short circuit and thus prevent thebuild-up of a sufficiently high voltage 'for reversal development.Further, the back of the photocopying material must be contactedelectrically in approximately the same areas to which developing liquidis supplied on the front. With this developing process, known methods,such as wiping over or passing through a container of liquid, do notproduce uniformly and faultlessly developed images. Other knownprocesses and devices for coating and photocopying purposes do notproduce satisfactory results either because of the different objectsthey are intended to achieve, and particularly because it is notpossible to make use of the differences in the mechanical properties ofthe surface of the material carrying the latent image, for exampleroughness, during the developing process. Only the differences in thefield intensity should be used for achieving the imagewise wetting ofthe material.

Further, the developing device should be designed in such a way that,although the amount of developer required for covering the entire areais available, the developing liquid, which has a low viscosity, can notflow out of or down from the device.

In the process of the present invention, a wetting developer is appliedto a material carrying an electrostatic field from a thin, linear slotwhich may be in contact with the surface of the material with at leastone of its boundary surfaces, and a relative motion is effected betweenthe surface and the slot.

The present invention further includes a device for carrying out theabove process, which device includes two substantially opposite boundarysurfaces forming a duct in which the wetting developer is contained, thecross-section of the duct being one-dimensionally extended and the ducthaving at least one open end during the developing process, whereas theother end may be connected to a reservoir, if desired.

One advantage of the device of the present invention is that the designthereof is very simple and that there are no complicated moving parts.This results in an easy and simple mode of operation with an extremelylow susceptibility to trouble. Further economical advantages result fromthe low maintenance costs thereof and its quick readiness for use.Through the process of the present invention, images of electric fieldsare obtained which exhibit very good covering power and sharpboundaries.

An electrostatic field is understood in the present invention to be aspace which is considered from the point of view of its electricalproperties and which surrounds an electrically effective body. The spacemay be filled with gas or with solid bodies, it may, however, also be avacuum. An electric field is considered to extend over a certain regionof space when the prevailing physical conditions guarantee that a smallelectrical test charge 2 would be exposed to a force K if it werebrought to any point of that region of space.

Such an electrostatic field may, for example, be produced by providingan organic or inorganic photoconductive coating, known inelectrophotography, with an electrostatic charge, differentiating thecoating by imagewise exposure if desired.

Imagewise modified electrostatic fields may also be produced byimagewise exposure of a suitable coating which is simultaneouslyprovided with a direct current voltage. The basic principles of thismethod are described in the book Photoelectrets and theElectrophotographic Process by V. M. Fridkin and I. S. Zheludev (1961),Library of Congress Catalog Card Number: 61-10020, and A. Kallman, B.Rosenberg: Persistent Internal Polarization Phys. Rev. 1955, pages1596-1610.

The process and the device according to the present invention will befurther illustrated by reference to the accompanying schematic drawingsin which:

FIGURES 1 and 2 show two embodiments respectively, of the device of thepresent invention in side elevation.

FIG. 1 is the simplest embodiment of the device. A strip of thinmaterial, for example sheet metal or another elastic or plasticmaterial, preferably having the Width of the sheets or webs to bedeveloped and a height of approximately 10-100 mm. preferably 30-50 mm.is connected to a shaped part 2, for instance a body fabricated from aplastic material or metal, in such a manner that the strip of material 1is extended over the end of the tapered part 2. This extension 3 may be1.0-8.0 mm. long, preferably 2.0-5.0 mm. Part 2 has a recess 4 whichserves as a reservoir for the developing liquid. A narrow tapered recess5 which is preferably provided with grooves is cut vertically into thefront of part 2 which is in contact with the flexible material 1. Therecess 5 is intended to serve as a resistance to the free fiow of thedeveloping liquid. At point 8 the flexible material 1 is secured to part2.

If the device of the invention is moved, in the direction indicated bythe arrow, across the surface 10 carrying the electrostatic field, theflexible material 1 is slightly lifted off the tapered part 2, anddeveloping liquid can flow through the now formed duct 6 to the lowerpart 7 of the device. The material 1 and the liquid are thereby indirect surface contact with the area to be developed.

FIG. 1 shows the device ready for use. When it is not being used, theflexible material 1 closes the duct 6, so that the developing liquid cannot flow out. The entire device can then be tipped back so that all thedeveloping liquid collects in the recess 4. When doing this, the fillingopening 9 is closed. It is however, not always necessary that part 1closes the duct 6 when the device is not being used. This is notrequired when the diameter of the duct 6 is so small that the surfacetension of the liquid is sufficient to prevent it from flowing out.

FIGURE 2 shows a further embodiment of the device of the presentinvention which produces preferred results. A container extendinggenerally over the entire width of the area to be developed andconsisting of solid material, preferably metal, is provided with anarrow linear duct 12 at its lower end and is directly connected to alarger reservoir 13. A smaller intermediate container 14 may be providedbetween the duct 12 and the storage container 13; the storage containeris provided with a filling opening 15. The opening of the duct 12 isdesigned to be so narrow that the surface tension of the developingliquid is sufiicient to prevent the liquid from running out when thedevice is not being used. Only the contact between the material to bedeveloped and the liquid which is retained at the discharge opening ofthe duct 12 by surface tension effects a continuous flow. Contactbetween the container 11 and the material to be developed is accompaniedby a relative motion, i.e. either the material, or the container 11, orboth are moved. As shown in FIG. 2, the material to be developed can befed to the device by means of a suitable auxiliary device. The material16 to be developed is moved over a feed table 17 in the directionindicated by the arrow, is seized by one or two feed rolls 18 and 18a,and is passed in contact with the aforementioned duct opening via amoistening device 19 having a cooperating pressure spring 20, ifdesired. The developed image is delivered at the other end of table 17.

If a reversal development is to be effected with the process and thedevice of the present invention, care should be exercised that a highertension can be applied during the wetting process between the developingliquid and the material carrying the electric field, possibly in thearea in which the wetting process takes place at any particular moment.Such processes can be carried out with good results with the device ofthe present invention.

For this purpose, one pole of a voltage source is connected to theflexible material 1 shown in FIG. 1, and the other pole to the metalsupporting plate 21. With the device according to FIG. 2 the two poleends are connected to the container 11 and the table 17. Potentials ofup to 800 volts may be applied. Short circuit or interruption of thecurrent will not occur either before, during, or after the developingprocess. With this method, it is an advantage that the contact betweenthe wetting developer and the material to be developed remains at alltimes under direct or immediate current contact.

The process and the device of the present invention make it possible todevelop electrophotographic material very quickly. Even with developingspeeds of approximately 20 cm. per second, excellent results areobtained. It is, however, also possible to increase or decrease thisspeed and then also very good image quality is obtained. It is possibleto develop both out sheets, for example DIN AS-DIN A1, or continuousmaterial from a roll. With the latter, feed rolls or similar deviceswhich transport the material to be developed when it emerges from thedeveloping zone are not required if the winding and unwinding devicesare controlled. With this method of working any number of prints can bedeveloped with absolute consistency.

It will be obvious to those skilled in the art that many modificationsmay be made within the scope of the present invention without departingfrom the spirit thereof, and the invention includes all suchmodifications.

What is claimed is:

1. A process for developing an electrostatic image on the surface of asheet of material comprising providing a liquid wetting developerdispenser carrying a supply of liquid wetting developer and including athin elongated discharge duct defined between a pair of spaced boundarysurfaces at least one of which is rigid and wherein liquid wettingdeveloper is preventing by surface tension from running out through saidduct except when said duct is adjacent an electrostatic field, passing asheet of material in contact with said one rigid boundary surface andcansing liquid developer to flow only onto those portions of the surfaceof the sheet having electrostatic charges thereon in a thin elongatedarea extending widthwise of the associated sheet, and moving saiddispenser relative to the surface of said sheet so as to very quicklydevelop the entire electrostatic image on said sheet.

2. A process as defined in claim 1 wherein said sheet remains stationaryand said dispenser is moved.

3. A process as defined in claim 1 wherein said dispenser remainsstationary and said sheet is moved.

4. A process as defined in claim 1 wherein both said dispenser and saidsheet are moved.

5. A process as defined in claim 1 wherein each of the boundary surfacesof said thin elongated discharge duct are rigid.

References Cited UNITED STATES PATENTS 1,950,351 3/1934 Clark et al118-410 2,368,520 1/1945 Burckhardt et al. 118-415 2,774,327 12/ 1956Saint-Hilaire 118-415 2,796,846 6/1957 Trist 118-410 2,841,827 7/1958Crownover 415 2,933,061 4/1960 Galer 3 3,051,125 8/ 1962 Ohara et al 6033,088,434 5/ 1963 Sprague et al 40 3,094,914 6/ 1963 Smith 401 3,096,1987/1963 Schatfert 37 3,168,021 2/1965 Levene 637 3,202,526 8/ 1965Ostensen 117-37 3,084,043 4/1963 Gundlach 117-37 X 3,245,381 4/ 1966Brenneisen et al. 117-37 X 3,276,424 10/1966 Marx et al. 117-37 X3,285,741 11/ 1966 Gesierich et al 117-37 X 3,060,429 10/1962 Winston11793.4 X

FOREIGN PATENTS 244,999 2/1963 Australia. 1,323,519 3/1963 France.

59,392 4/ 1891 Germany. 134,963 5/ 1901 Germany. 391,188 6/ 1923Germany.

WILLIAM D. MARTIN, Primary Examiner.

E. J. CABIC, Assistant Examiner US. Cl. X.R.

1. A PROCESS FOR DEVELOPING AN ELECTROSTATIC IMAGE ON THE SURFACE OF ASHEET OF MATERIAL COMPRISING PROVIDING A LIQUID WETTING DEVELOPERDISPENSER CARRYING A SUPPLY OF LIQUID WETTING DEVELOPER AND INCLUDING ATHIN ELONGATED DISCHARGE DUCT DEFINED BETWEEN A PAIR OF SPACED BOUNDARYSURFACES AT LEAST ONE OF WHICH IS RIGID AND WHEREIN LIQUID WETTINGDEVELOPER IS PREVENTING BY SURFACE TENSION FROM RUNNING OUT THROUGH SAIDDUCT EXCEPT WHEN SAID DUCT IS ADJACENT AN ELECTROSTATIC FIELD, PASSING ASHEET OF MATERIAL IN CONTACT WITH SAID ONE RIGID BOUNDARY SURFACE ANDCAUSING LIQUID DEVELOPER TO FLOW ONLY ONTO THOSE PORTIONS OF THE SURFACEOF THE SHEET HAVING ELECTROSTATIC CHARGES THEREON IN A THIN ELONGATEDAREA EXTENDING WIDTHWISE OF THE ASSOCIATED SHEET, AND MOVING SAIDDISPENSER RELATIVE TO THE SURFACE OF SAID SHEET SO AS TO VERY QUICKLYDEVELOP THE ENTIRE ELECTROSTATIC IMAGE ON SAID SHEET.